1. Field of the Invention
The present invention relates to a DC-DC converter.
2. Description of the Background Art
In a power step-up DC-DC converter that handles a high voltage and a large current, a switching frequency by a chopper circuit is increased, whereby efficiency enhancement and downsizing of a device can be achieved. However, the increase of the frequency results in an increase of a switching loss of a power semiconductor element that performs switching. Accordingly, from a viewpoint of the switching loss, the increase of the frequency becomes a cause to inhibit the efficiency enhancement and downsizing of the device. Note that such a problem is not limited to the power step-up converter.
In order to reduce the switching loss, a soft switching circuit is sometimes used. In Japanese Patent Application Laid-Open No. 2004-201369, there is described a soft switching circuit for reducing a switching loss at the time when a switching element is turned off.
However, in the soft switching circuit of Japanese Patent Application Laid-Open No. 2004-201369, a switching loss at turn-on cannot be reduced. Specifically, when the switching element is turned on, the switching element causes hard switching owing to a recovery current of a diode.